1. Field of the Invention
The present invention relates to industrial machinery, and, in particular, to industrial gas turbines and operation thereof. More particularly, the present invention provides a sys tem for electronically controlling the operation of gas turbine engine bleed valves.
2. Description of Related Art
Gas turbines serve a variety of important purposes (e.g., generating electricity; pumping oil; compressing natural gas, turning a ship's propeller), and operate by converting thrust power into shaft or rotary power to turn or “drive” one or more pieces of industrial machinery.
The engine of a gas turbine is a rotary or axial type engine that spins around a common shaft located in the center of the engine. Several sections comprise the engine along that shaft, including a compressor section, a combustion section and a turbine section.
The compressor section is the front-most section of the gas turbine engine, and is comprised of a plurality of bladed disks that compress inlet air, which generally is supplied to the compressor section as air from the outer vicinity of the compress or (e.g., outside air). The compressor section of the gas turbine engine is divided into two related, but separate parts—a low-pressure compressor, and a high-pressure compressor, which act in concert to compress the supplied air, and to direct the compressed air to the adjacent combustion section of the gas turbine engine.
In the combustion section of the gas turbine engine, the compressed air that is received from the compressor section is mixed with fuel and then ignited to create expanding gases, which, in turn, are directed/fed into the turbine section of the gas turbine engine.
The turbine section of the gas turbine engine includes a plurality of wheeled blades, which comprise high and low turbines that are turned by the hot expanding gases from the combustion section. The high and low turbines drive the low- and high-pressure compressors through the action of common shafts, thus creating and maintaining a continuous combustion cycle of the gas turbine engine.
There are several problems with conventional rotary gas turbine engines—especially twin axial compressor type engines—that arise during the acceleration and deceleration of the engine, most notably a mechanical lag/delay between the high and low turbine sections that are being driven by the expanding combustion gases.
This momentum delay causes the high- and low-pressure compressors to turn at different rates, and that, in turn, has the effect of trapping unused compressed air between the low- and high-pressure compressors. This trapped air condition—if unalleviated—will partially or completely halt the rotation of the compressor blades, thus causing the engine to undergo “compressor stall.” Compressor stall, in turn, causes associated engine vibration, which, if recurrent, will ultimately lead to compressor and/or engine failure.
Those in the art have routinely installed so-called “bleed valves” (or some other like mechanism/equipment) between the low-pressure and high-pressure compressor sections of the gas turbine engine. In general, a bleed valve is a valve or series of valves mounted to the compressor section of the gas turbine engine and operated to “bleed away” excessive compressor air, thus at least minimizing (if not entirely avoiding) the occurrence of “compressor stall.”
During operation of a bleed valve system, one or more bleed valves open in order to bleed off some of the “stalled” air and to smooth the vibration of the gas turbine engine that is caused by the compressor having stalled during acceleration and deceleration of the engine. The bleed valves then close once the engine has reached a constant speed, thus allowing the engine to resume operation at or closer to maximum efficiency.
Conventional industrial gas turbine engine bleed valve systems (e.g., the Pratt & Whitney GG4 system) are modeled after valve systems used in jet engines of airplanes. In both settings, the systems are comprised of pneumatically actuated valves that open and close in response to different pressures.
To enable this to occur, pressure sensing lines supply compressor air to bleed valve actuators, and an internal pressure valve assembly senses the compressor air pressure and controls the actuators, which are prompted to move back and forth, causing the bleed valves to open or close. A valve assembly (i.e., a damper) mounts above an opening between the high- and low-pressure compressors. When the valve assembly is open, it allows excess air to bleed from between the high- and low-pressure compressors, after which it closes to allow the compressors (and, thus, the engine) to operate at or closer to maximize efficiency.
Existing bleed valve systems are generally comprised of a plurality of bleed valves (usually three bleed valves—a left bleed valve, a center bleed valve, and a right bleed valve), which are mechanically set to operate at different pressures, and which are controlled by respective bleed valve actuators. The actuators include internal valves that sense the pressure (which is mechanically set with springs and shims) of the compressor air supplied from the pressure sensor lines, and open or close the actuators to operate the attached butterfly valve.
If the opening and closing of each bleed valve is timed correctly, incorporation of the bleed valve system within the gas turbine engine should be effective to smooth the vibration of the gas turbine engine, yet not compromise the engine's operating efficiency.
However, although conventional gas turbine engine bleed valve systems have proven effective to at least somewhat smooth the vibration of gas turbine engines, the timing of the opening and closing of the various bleed valves has not allowed for an ideal balance between smooth vibration and engine efficiency.
Another shortcoming of conventional gas turbine engine bleed valve systems stems from the fact that although their design is similar to that of valve systems used in connection with flight jet engines, their usage environment is very different. Specifically, whereas flight jet engines are operated primarily at altitudes thousands of feet above sea level, where the air is both dry and clean (and, thus, compressible), gas turbine engines are operated at or below sea level, where the air is generally unclean and moisture-laden (and, thus, incompressible).
Over time, circulation of moisture-laden, incompressible air through a gas turbine engine compressor and into a series of bleed valves will result in degradation of the bleed valves, which, in turn, will either require costly repair of the bleed valves, or, if unnoticed, will cause premature valve failure. In a similar vein, the dirt and moisture contained in the air can cause friction, which, in turn, can necessitate costly repair, or lead to failure of the springs, shims and/or spacers that comprise the pressure actuators and enable them to function properly.
Therefore, a need exists for an improved bleed valve system that enables a more streamlined, optimal operation of the bleed valves that are incorporated within a gas turbine engine, yet that can be utilized in connection with existing gas turbine engines. A further need exists for such a system to be operable in a wide variety of usage environments—even those where the outside air is polluted, dirty and/or moisture-laden—without fear of necessitating expedited repair of the system's components and/or shortening the lifetime of the system.